The present invention relates to a process for treating the surface of aluminum and its alloys. It is a prime object of this invention to provide a protective coating having desirable appearance, high corrosion resistance and high adhesion of top coated paints on the surface of aluminum and its alloys for cans, building materials, automobiles, electric appliances and the like.
The surface of aluminum and its alloys has conventionally been treated with a strong alkaline etching cleaner solution, rinsed with water and then chromated or oxidized anodically. The chromating process has well-known environmental and health disadvantages due to the presence of chromium. The anodizing process requires large and expensive equipment and a large amount of power, and is therefore economically undesirable.
U.S. Pat. Nos. 3,975,214 and 4,054,466 disclose metal treatment processes employing aqueous organic tannin solutions.